Vehicle security systems can be classified into a passive security system and an active security system. The passive security system such as airbag or high-rigidity vehicle body is configured to initialize the protecting mechanism while after a vehicle collision occurs, whereas the active security system initializes the protecting mechanism whenever there exist potential danger so as to reduce or eliminate the risk of vehicle colliding. The active security system includes system measuring distances between vehicles by utilizing radar electromagnetic waves, image processing, or radar detection, thereby assisting drivers to determine the proper driving speed and directions.
However, the energy in radar electromagnetic waves decreases under pouring rain. Also, under pouring rain, there exists cross-polarization interference problem caused by scattering effect, which leads to inaccurate detection. Other detection method such as image processing and radar detection will also be affected by bad weather condition, which also leads to inaccurate detection. Therefore, no matter what detection method is chosen, the accuracy of the detection is susceptible to weather condition, which leads to drivers' misjudgments and possible danger.